(1) Field of the Invention
The present invention relates to an agricultural covering material generally called "mulch film".
(2) Description of the Prior Art
In the mulch cultivation, a mulch film is used for elevating the ground temperature, retaining water in soil, preventing caking of soil, preventing effluence of nutrients and preventing growth of weeds.
A mulch film composed of high-pressure method low-density polyethylene or a blend of high-pressure method low-density polyethylene and an ethylene/.alpha.-olefin random copolymer rubber is known (see Japanese Patent Application Laid-Open Specification No. 116735/81).
However, the mechanical strength of the mulch film composed of high-pressure method low-density polyethylene is low and therefore, the thickness should be increased beyond 20 .mu.m. For example, when a film is formed at a blow ratio exceeding 2 and the thickness is adjusted to less than 20 .mu.m, the tear strength is low and the film is readily broken or torn when the film is spread or dismantled. On the other hand, if the film thickness is larger than 20 .mu.m, the Young's modulus is increased and the film becomes stiff, and the film fails to adhere tightly to the solid surface of a levee and an air layer is readily formed between the film and soil. Accordingly, growth of weeds is promoted and cultivation plants are damaged by fluttering of the film by a wind or rain.
Furthermore, this mulch film is insufficient in the heat resistance, and if the film is a so-called perforated mulch film holes are expanded while the film is used and the capacity of the film as the covering material is reduced.
Moreover, the mulch film composed of a blend of high-pressure low-density polyethylene and an ethylene/.alpha.-olefin copolymer rubber is insufficient in the weatherability and long-run formability and is not satisfactory in the strength, transparency and surface characteristics such as the gloss.